Transmission Slipping? (intermittent loss of power feeling when flooring it)

2006 Prerunner 4.0L V6

I have had the truck about 2 years now. I initially had shudders (rumble strip vibrations) from gear 3-4 around 33mph when I first purchased the truck. I did a full flush by dropping the pan, new filter, cleaned magnets, etc. and 14 qts of amsoil's OE trans fluid, a tube of shudder fix, and a bottle of lubeguard. The shudder was immediately gone and it has only done it once since (I think, could have been the road I was on).

I drove like an old man for most of the time I owned the truck, with nothing weird with the trans. I do sometimes get shudders when decelerating around 35-40mph but it's done that since day 1.

I recently got in the habit of being much harder on the gas because I was sick of how early the truck shifted. When I mostly floor it (close to or all the way to the carpet) I get a lot of hesitation above gear 3 where it feels like the truck loses a lot of power for a moment, then picks up again, then loses power. It does eventually shift into higher gears, and has no issues with shifting unless I'm flooring the accelerator.

My question(s) are:
1.) Am I driving a time bomb with my trans?
- I know I've heard some vehicles will drive for years still with a slipping trans, others not

2.) Does this likely mean the trans is slipping or is this normal behavior when trying to floor it with these trucks?

3.) Did using non-"WS" trans fluid cause this? Should I do a full flush and replace with Toyota WS trans fluid or a synthetic that is recommended and known to be comparable to Toyota's "WS" standards?
- I have heard many people swear by not deviating from this fluid, and that Amsoil's OE fluid doesn't have the same properties.

4.) Did using the shudder fix or lubeguard mess with the transmission? I also followed instructions to turn an allen wrench on a solenoid 1/4 clockwise to increase engagement pressure back when it was shuddering. Again it has no problems and hasn't had any since until I started flooring it and noticing this weird slipping (hopefully not actually) feeling.

I did a fluid level check by adding 1/2 a quart and doing the trans temp jump with the connector, as much fluid as I put in came back out (minus a little loss when I had replaced the transmission output shaft seal a few weeks back.) The truck still did the same thing when flooring it above 30ish MPH. It's either me over-worrying, or time to get a new truck. Thanks!

 

You should be able to tell if it's slipping by watching your tach, if the tach suddenly goes up rapidly but the truck isn't accelerating then it's slipping.

 

Having a transmission rebuilt by a reputable independent shop isn't that expensive. $2000-$3000. It's more cost effective to just drive it and never change the fluid. Your truck is 18 years old. If you paid to have it changed every other year, you'd have paid $2000-$3000 to keep the transmission serviced. Chances are good it wouldn't last a day longer even if you do the work yourself at reduced costs.

You don't mention miles, but on a truck that old I'd have never done anything to the transmission. I'd have just kept driving it till it died then get it rebuilt. At best you just put a band-aid on a dying transmission. At worst you sped up its demise. Either way that was wasted money.

 

@Dm93 I will have to pay close attention to that next time I drive.

@Marshall R Good point, it has 135k miles and was about 10k less when I did the fluid change.

 

The Amsoil OE Mult-Vehicle doe NOT say it is compatible with WS fluid.

The OE "Fuel Efficient" and "Signature Series" are WS compatible.

I'd go with Valvoline MaxLife over Amsoil. Because it's better than WS and cheaper than Amsoil.

As for slipping, do what Dm93 said. Look at the tach and see what is happening.

 

@TnShooter I will keep an eye on it next week when I'm back home and driving, will have an answer Monday.

Regardless of the result, I checked my order and I see I did put in the non-WS compatible fluid (multi-vehicle).

Would I be doing more harm than good to do a flush and put in the correct fluid? Should I do a few drain and fills over time? Or just leave it and wait for the bomb to go off?

Thank you!

 

I'd say let's confirm weather or not the transmission is slipping, if it is then changing the fluid probably won't help you. If it's not then consider putting the correct fluid in.

 

@Dm93 @TnShooter I come bearing hopefully good news... so the Tach does not to seem to shoot up or rapidly rise when it does get the weird "bogged down" feeling when accelerating quickly.

What's the next list of likely things? Air/Fuel/Spark issue? Slow acceleration there is no issue, 3/4 pedal to floor seems to be where it happens the most, as I fully floored it a few times to the floor and it did not appear to do it either. I have no codes, engine air filter is pretty clean < 2 years old.

It kind of feels like when you have a bad air/fuel mixture on a carbureted bike and it hesitates (slows/loses power) on and off when trying to floor it.

I will re-confirm a few more times and then plan to swap in the correct fluid if it's not slipping.

 

So it sounds more like an engine issue than a transmission issue.

Do you have any CEL or codes?

Do you have a scan tool that can read and graph live data?

 

@Dm93 I do not have any codes, I would likely have to rent or buy a fancier scan tool to see if I can pick anything up on live data, any budget friendly recommendations?

 

Just a random spitball, but I wonder if maybe a plugged catalytic converter? Guessing you are still on the originals?

Don't go replacing it on my guess but this sounds just like what happened with an old car my father had.

 

I mean it depends what you want it to do and what your budget is, I'm biased toward all system bi-directional scan tools because they are pretty much required anymore to do any real diagnostics on a modern vehicle. They have come down in price alot over the past few years but your still in the $500+ range for a good one unless you go with a Bluetooth based one that connects to a smartphone. There are only 2 that I know of in this category, they are both around $90 plus a subscription.

An all systems non bi-directional scanner is gona be in the $250-400 range.

A basic graphing scan tool you should be able to find for $150 or less.

I'd take a look at the offerings from Launch, TopDon, and Autel and see what fits your needs and budget.

 

Certainly a possibility, you would need to pull the upstream O2 sensors one at a time and screw in an exhaust backpressure tester to verify or use an in cylinder pressure transducer and oscilloscope.

 

What little I recall of it, there was no CEL (or maybe not yet/pending code, as I didn't have a reader then). He brought it to a shop and they diagnosed/replaced it, no more trubs.

 

They typically won't throw a code if they are plugged, I can diagnose them pretty accurately with just scan data and how the vehicle sounds but I always take a pressure gauge and verify. I've seen alot of plugged cats mis-diagnosed and a long list of parts thrown at them though lol.

 

that would be called a lean bog ( power falls way off as you hit the throttle and a second or two later snaps back with authority) and as the name implies is often due to a mixture thate is too lean for the acceleration rate being demanded (i.e. a accelerator pump issue on a carb), though other things can create similar symptoms.

accell enrichment makes sense given your description that slow throttle application is good and rapid is bad.

modern maf based ecus use throttle position mostly for accell enrichment, so I would be looking at maf and tp behavior as i hit 3/4 throttle. While failing coils can mimic this, it would not create a systemic problem on COP setups.

 

Doesn’t seem too likely basec on symptoms. Op says full throttle application creates good performance, but 3/4 throttle application creates the bog. A plugged cat would not present like this IMHO

 

The best way is to use AFR/O2 data for a low power complaint, if we see them go lean during the low power issue we start looking at fuel and MAF. If we see them go rich then we check for a plugged exhaust.

 

Learned something new today have I. Only other experience with them I have had was a few years ago with my wife's old Rav4, it sounded a little loud so I crawled under and had her start it. Converter outside shell was rotted, replaced it and moved on.

My Tacoma was running fine but it had a recall for the converters a while ago..just gave em the keys and they did it.

Agreed I'd be more likely to suspect other things first, in general. But it's not totally off the table, I reckon I should have said I would add it to the list of possibles that he listed re air/fuel/spark.

 

Excellent advice here! If found to be lean and with your symptoms (bog occurs only under aggressive acceleration), I would definitely add throttle position data to that list. ECU relies upon TP to determine the amount of additional fuel needed to deal with rapid throttle advancement. maf is inadequate for this task.